1. Field of the Invention
The present invention relates to a circuit molded structure having bus bars forming internal circuits.
The present application is based on Japanese Patent Application No. Hei. 10-99564, which is incorporated herein by reference.
2. Description of the Related Art
A circuit molded structure, having bus bars serving as internal circuits, has been used in an electric part such as a connector. For molding the circuit molded structure, a plurality of bus bars are inserted in a mold, and in this condition, a resin is molded to form a primary molded member or body holding the plurality of bus bars in non-contact relation to one another, and then a resin is secondarily molded on the primary molded body, thereby forming the circuit molded structure.
FIG. 5 shows a primary molded member 1 having a plurality of bus bars 2 insert-molded therein. In order that terminal portions 2a of the bus bars 2 may be arranged at a predetermined pitch and that the secondary molding operation may be effected easily, each bus bar 2 has an L-shaped bent portion 5. In the primary molded member 1, generally the whole of each bus bar 2 except the terminal portion 2a is held by a hold portion 3. Therefore, the resin is molded also on the bent portion 5 of the bus bar 2.
In the primary molded member 1 thus formed, however, the bus bar 2 is liable to tilt inwardly as at A (see FIG. 6) at one side of the bent portion 5 when the resin, forming the hold portion 3, shrinks. Even if the primary molded member 1, subjected to such inward tilt A, is set in a mold 4 for effecting the secondary molding, the primary molded member 1 interferes with the mold 4 at a portion indicated by B in FIG. 7. Therefore, there has been a possibility that the secondary molding is not be properly carried out.
Accordingly, there has heretofore been used the type of primary molded member in which the bent portions 5 of the bus bars 2 are not covered with the resin. FIG. 8 shows such a improved primary molded member 6 in which a hold portion 3 is divided into a hold section 3a and a hold section 3b provided respectively on opposite sides of a bent portion 5 of each bus bar 2, and the bent portion 5 is not covered with the resin, and therefore is exposed. With this construction, the inward tilting of the bus bars 2 due to shrinkage of the resin is prevented.
In FIGS. 9 to 12, a resin is secondarily molded on the improved primary molded member 6, thereby integrally forming a secondary molded member 7 on the primary molded member 6, thus forming a circuit molded structure 8 such as a connector-incorporating case. As shown in FIGS. 9 and 11, the primary molded member 6 has a construction in which the bent portions 5 of the bus bars 2 are not covered with the resin, and this primary molded member 6 is set in a mold (not shown) for effecting the secondary molding, and the resin is secondarily molded. As a result, as shown in FIGS. 10 and 12, there is formed the circuit molded structure 8 in which the secondary molded member 7, having a board mounting portion 9 and a connector portion 10 disposed perpendicular to the board mounting portion 9, is integrally molded on the primary molded member 6.
In this circuit molded structure 8, the board mounting portion 9 and the connector portion 10 of the secondary molded member 7 are disposed perpendicular to each other through an interconnecting portion 11. A printed circuit board (not shown) is mounted on the board mounting portion 9, and a mating connector (not shown) is fitted into the connector portion 10 so as to make an electrical connection. Each bus bar 2 of the primary molded member 6 is provided in the board mounting portion 9 and the connector portion 10, and the bent portion 5 of the bus bar 2 is disposed in the interconnecting portion 11 of the secondary molded member 7.
However, in the circuit molded structure 8, the bent portions 5 of the bus bars 2 are exposed, and the resin is liable to flow to the bent portions 5 during the secondary molding, and as a result that portion (indicated by C in FIG. 10) of the interconnecting portion 11 of the secondary molded member 7, corresponding to the bent portions 5, becomes greater in thickness than the remainder of the interconnecting portion 11, so that the thickness difference develops between these portions. If such thickness difference is encountered, there develops a time lag in expansion and shrinkage of the resin between these portions, so that internal stresses increase, and therefore a thermal shock resistance is lowered. As a result, cracks 12 develop in the interconnecting portion 11.
And besides, during the secondary molding, the bent portions 5 of the multi-pole bus bars 2 are disposed at the interconnecting portion 11 in an exposed manner, and heat, developing during the secondary molding, is transferred to the hold portions 3a and 3b of the primary molded member 6 through the exposed bent portions 5, and resides in these hold portions 3a and 3b. Therefore, those portions of the molded structure, having the hold portions 3a and 3b of the primary molded member 6, and that portion (corresponding to the bent portions 5), having only the resin of the secondary molding, are different in contraction coefficient (shrinkage factor) from each other. Therefore, the above-mentioned cracks 12 are more liable to develop.
In the case where each of the primary molded member 6 and the secondary molded member 7 is molded of a resin containing glass fibers, the orientations of the glass fibers are different from one portion to another depending on the specification of the molded product. More specifically, if the glass fibers of the hold portion 3b of the primary molded member 6 are oriented in a direction 13 (see FIG. 11), the glass fibers of the interconnecting portion 11 of the secondary molded member 7, corresponding to the hold portion 3b, are oriented in a direction 14 (see FIG. 12). Thus, the orientation directions 13 and 14 are different from each other. If the orientation directions of the glass fibers of the two portions are thus different from each other, these portions of the molded product are different in contraction coefficient from each other, and therefore cracks due to a thermal shock develop in these portions.